Unicornuate Uterus: Symptoms, Types, Causes and Treatment

The unicornuate uterus is a rare congenital uterine anomaly that can have profound implications for a woman’s reproductive health, fertility, and pregnancy outcomes. Understanding the symptoms, classifications, underlying causes, and available treatments is crucial for both patients and healthcare providers. In this article, we break down the latest evidence-based knowledge about unicornuate uterus, integrating clinical findings and research insights to provide a clear, comprehensive guide.

Symptoms of Unicornuate Uterus

The symptoms of a unicornuate uterus are often subtle or even absent until adolescence or reproductive years. Recognizing these symptoms is vital for early diagnosis and management, as this condition can be associated with significant gynecological and obstetric complications.

Symptom	Prevalence/Characteristic	Associated Risks	Source(s)
Pelvic pain	Common with non-communicating horn	Endometriosis, hematometra	1 6 8
Dysmenorrhea	Severe if functional rudimentary horn	Endometriosis, hematometra	6 8
Infertility	Present in some cases (14%)	Ectopic pregnancy, miscarriage	3 10
Recurrent miscarriage	Frequent in affected women	Preterm birth, fetal loss	5 7 10
Ectopic pregnancy	Increased risk	Uterine horn rupture, emergency	2 3 12 14
Renal anomalies	Often associated	Unilateral renal agenesis	1 3 9

Table 1: Key Symptoms

Pelvic Pain and Dysmenorrhea

• Pelvic pain is a hallmark symptom, especially in women with a non-communicating, functional rudimentary horn. This pain typically worsens with menstruation (cyclic pain) and may be severe, particularly in adolescents soon after menarche. The cause is often hematometra (trapped menstrual blood) in the non-communicating horn, which can lead to secondary endometriosis due to retrograde menstruation 1 6 8.
• Dysmenorrhea (painful periods) is often more severe in these cases and may be accompanied by symptoms like catamenial dysuria or hematuria if there is associated endometriosis involving the bladder 6 8.

Infertility and Pregnancy Complications

• Infertility is reported in about 14% of women with a unicornuate uterus, though many can conceive. However, conception is often complicated by a higher risk of ectopic pregnancy, miscarriage, and preterm birth 3 10.
• Recurrent miscarriage and preterm delivery are significant risks, particularly when embryo implantation occurs in an abnormal uterine environment. These risks are amplified in women undergoing assisted reproductive techniques like IVF 5 7 10.

Ectopic Pregnancy and Acute Complications

• Ectopic pregnancy is much more common, especially if a rudimentary horn is present, and may lead to life-threatening uterine horn rupture, often in the first or early second trimester 2 3 12 14. Early recognition and intervention are crucial for maternal safety.

Renal and Urinary Tract Anomalies

• Up to 40% of women with unicornuate uterus have associated renal agenesis (missing kidney) or other anomalies, often on the side opposite the rudimentary horn 1 3 9. This association is due to the shared embryological origin of the urinary and reproductive tracts.

Types of Unicornuate Uterus

Unicornuate uterus is not a single uniform condition. Its anatomical variants significantly affect clinical management and prognosis. The main subtypes are defined by the presence, size, and communication of a rudimentary horn.

Type/Subtype	Description	Clinical Relevance	Source(s)
Isolated unicornuate uterus	Single small uterine cavity, no horn	May be asymptomatic, better outcomes	1 3 4
With rudimentary horn: non-communicating, functional	Horn contains endometrium, no uterine access	Pain, endometriosis, rupture risk	1 6 8 12 14
With rudimentary horn: communicating	Horn connects to main cavity	Less severe symptoms, rare	1 4
With rudimentary horn: non-functional	No endometrium in horn	Often asymptomatic	1 3 4
Associated anomalies (e.g., renal agenesis, ectopic ovary)	Frequently co-occurring	Complicates management	1 3 9

Table 2: Unicornuate Uterus Types

Isolated Unicornuate Uterus

• Isolated form involves a single, banana-shaped uterine cavity with no rudimentary horn. These cases may remain undiagnosed unless complications like infertility arise. Prognosis is generally better as there is no risk of hematometra or rupture 1 3 4.

Unicornuate Uterus with Rudimentary Horn

• Non-communicating, functional horn is the most dangerous variant. The rudimentary horn contains functional endometrium but has no connection to the main uterine cavity, leading to trapped menstrual blood, pain, and a high risk of complications such as endometriosis and rupture during pregnancy 1 6 8 12 14.
• Communicating rudimentary horn means that the accessory horn is connected to the main cavity. Symptoms may be mild or absent, but complications can still arise 1 4.
• Non-functional horn lacks endometrial lining and is usually asymptomatic, sometimes discovered incidentally 1 3 4.

Associated Renal and Ovarian Anomalies

• Renal agenesis (missing kidney) and ectopic/undescended ovaries are frequently associated, reflecting the shared developmental pathways of the reproductive and urinary systems. Their presence can complicate the clinical picture and influence treatment choices 1 3 9.

Causes of Unicornuate Uterus

Understanding what causes a unicornuate uterus provides insight into its associated anomalies and potential complications. This condition is rooted in embryological development and can be influenced by genetic and environmental factors.

Cause/Mechanism	Description	Associated Findings	Source(s)
Müllerian duct maldevelopment	Failure of one duct to develop or migrate	Rudimentary horn, renal anomalies	1 9 8
Multifactorial polygenic factors	Genetic predisposition	Familial clustering, variability	9
Familial inheritance	Observed in some cases	Recurrence in families	9
Associated syndromes	VACTERL, Mayer-Rokitansky-Küster-Hauser	Multi-system anomalies	8 9

Table 3: Causes of Unicornuate Uterus

Embryological Origin

• The Müllerian ducts are paired embryonic structures that form the female reproductive tract. A unicornuate uterus results from the failure of one Müllerian duct to develop, fuse, or migrate correctly. This underdevelopment may lead to a single uterine cavity (the unicornuate uterus) and, in some cases, a rudimentary horn representing the incomplete duct 1 9.

Genetic and Familial Factors

• Evidence suggests a multifactorial polygenic inheritance, where multiple genes and possibly environmental factors contribute to the anomaly. Familial cases have been reported, but most cases are sporadic 9.

Associated Syndromes

• The unicornuate uterus can occur as part of broader congenital syndromes, such as VACTERL association (Vertebral, Anal, Cardiac, Tracheoesophageal, Renal, and Limb anomalies) or Mayer-Rokitansky-Küster-Hauser syndrome, which may include additional malformations of the urinary, skeletal, or other systems 8 9.

Developmental Timing

• The condition arises during the third month of fetal life, coinciding with the descent of the ovaries and formation of the urogenital system. Disruptions at this stage can explain the frequent association with renal and ovarian abnormalities, such as ectopic or undescended ovaries 9.

Treatment of Unicornuate Uterus

Management of unicornuate uterus is tailored to the type, presence of symptoms, reproductive goals, and associated complications. While some women may never need intervention, others require complex surgical or reproductive treatments to manage symptoms or reduce risks.

Treatment Option	Indication	Outcome/Prognosis	Source(s)
Surgical removal of rudimentary horn	Non-communicating, functional horn, pain, or pregnancy	Relieves symptoms, prevents rupture	6 8 11 12 14
Methotrexate + laparoscopic excision	Early pregnancy in rudimentary horn	Preserves fertility, safe outcome	14
IVF-ET (In vitro fertilization)	Infertility	Lower live birth, higher miscarriage	5 7 10
TCUI (Transcervical uterine incision)	Recurrent miscarriage, infertility	Improved term/live birth rates	13
Expectant/monitoring	Asymptomatic cases without functional horn	May not need intervention	1 3 4
Cesarean section	Pregnancy in unicornuate uterus	Reduces risk of rupture	12 14

Table 4: Treatment Options

Surgical Approaches

• Rudimentary horn removal is the mainstay treatment for women with a non-communicating, functional horn. This procedure alleviates pain, prevents life-threatening rupture during pregnancy, and reduces the risk of endometriosis 6 8 11 12 14. The surgery is typically performed laparoscopically for lower morbidity.
• If the rudimentary horn contains a pregnancy, local methotrexate injection can be used to stop fetal development, followed by delayed surgical removal to minimize bleeding risks 14.

Reproductive Assistance

• IVF-ET (In vitro fertilization-embryo transfer) is often used for women with infertility. Live birth rates are lower and miscarriage rates higher compared to women with normal uterine anatomy, particularly in fresh day-3 embryo transfers. Outcomes improve with blastocyst transfer and careful cycle management. Twin pregnancies should be avoided due to high risk of preterm birth and perinatal complications 5 7 10.
• TCUI (Transcervical uterine incision) is an emerging procedure that can increase the size of the uterine cavity and improve pregnancy outcomes for women with infertility or recurrent miscarriage. It has been shown to reduce first-trimester miscarriage rates and increase term delivery and live birth rates 13.

Obstetric Management

• Women with a unicornuate uterus who do conceive require close obstetric monitoring. Cesarean section is often recommended to prevent uterine rupture, especially if there is a history of horn excision or other risk factors 12 14.
• Expectant management is appropriate for women who are asymptomatic and have no functional rudimentary horn, but detailed evaluation and patient education are essential 1 3 4.

Management of Associated Anomalies

• Renal and ovarian anomalies should be identified through imaging and managed accordingly. Renal agenesis may require additional monitoring for hypertension and renal function throughout life 3 9.

Conclusion

The unicornuate uterus is a complex congenital anomaly with significant gynecological and obstetric implications. Early diagnosis and tailored management can dramatically improve outcomes for affected women. Key points include:

• Symptoms often include pelvic pain, severe dysmenorrhea, infertility, recurrent miscarriage, and increased risk of ectopic pregnancy, especially with a functional rudimentary horn.
• Types vary based on the presence and characteristics of a rudimentary horn, with non-communicating, functional horns posing the greatest risk.
• Causes are rooted in developmental errors of the Müllerian ducts, often with genetic and multifactorial contributions, and may be linked to broader syndromes.
• Treatment ranges from surgical intervention (especially horn removal) to reproductive techniques and vigilant pregnancy monitoring, with emerging procedures offering new hope for improved outcomes.

Summary of Key Points:

• Unicornuate uterus is rare but can have serious consequences if untreated.
• Symptoms and risks depend on the specific anatomical variant.
• Early, accurate diagnosis—often with imaging—is essential.
• Surgical removal of the rudimentary horn prevents major complications.
• Assisted reproduction and new surgical techniques can improve fertility outcomes.
• Ongoing monitoring is critical for pregnancy safety and to manage associated anomalies.

Women diagnosed with a unicornuate uterus can, with appropriate care, achieve good reproductive outcomes and improved quality of life.